stratum1

Stratum 1 refers to a level in the Network Time Protocol (NTP) hierarchy. Stratum 1 time servers obtain their time directly from a reference clock, such as a GPS, GLONASS, or atomic clock, which is classed as Stratum 0. The Stratum 1 server disciplines its local oscillator to track that reference time and then serves time data to clients on a network. In NTP, the stratum value increases by one for each hop away from the reference clock, so a Stratum 2 server gets time via a Stratum 1 server, and so on. Stratum 15 is the practical upper limit; a server at Stratum 16 is considered unsynchronized.

Most organizations run one or more Stratum 1 servers to provide accurate time within their networks or to external clients. Stratum 1 servers typically use high-stability hardware such as GPS receivers or cesium clocks and rely on holdover techniques if the reference clock becomes temporarily unavailable. They distribute time using the NTP protocol, which operates with UDP port 123 and supports various modes including client, server, and symmetric active/passive configurations.

Public time services, such as national or academic timekeeping infrastructures, may publish Stratum 1 sources that other devices can synchronize to, either directly or via pools like pool.ntp.org. Time accuracy at Stratum 1 can be affected by the quality of the reference clock, network latency, and server configuration, so redundancy and monitoring are common practices.

Security considerations include potential spoofing, jitter, and denial-of-service risks. Operators often implement authentication (NTP Autokey or symmetric keys), monitor offset and jitter, and use diverse reference clocks and multiple Stratum 1 servers to improve resilience.